Rear-wheel drive shaft

Abstract

A rear-wheel drive shaft (1) includes a fixed type constant velocity universal joint (3), a plunging type constant velocity universal joint (2), and an intermediate shaft (4) coupling both the constant velocity universal joints to each other. A ratio (PCDBALL(f)/DBALL(f)) of a pitch circle diameter (PCDBALL(f)) of balls (33) of the fixed type constant velocity universal joint (3) to a diameter (DBALL(f)) of each of the balls (33) is set from 3.70 to 3.87. A ratio (PCDBALL(s)/DBALL(s)) of a pitch circle diameter (PCDBALL(s)) of balls (23) of the plunging type constant velocity universal joint (2) to a diameter (DBALL(s)) of each of the balls (23) is set from 3.3 to 3.6.

The invention claimed is: 
     
       1. A rear-wheel drive shaft, comprising:
 a fixed type constant velocity universal joint comprising:
 a first outer joint member having a spherical inner peripheral surface in which eight track grooves extending in an axial direction of the fixed type constant velocity universal joint are formed; 
 a first inner joint member having a spherical outer peripheral surface in which eight track grooves extending in the axial direction of the fixed type constant velocity universal joint are formed, and having a spline hole formed along an axial center of the first inner joint member; 
 eight balls arranged in ball tracks formed by the track grooves of the first outer joint member and the track grooves of the first inner joint member; and 
 a first cage, which has eight pockets configured to receive the balls of the fixed type constant velocity universal joint, and is held in slide contact with the spherical inner peripheral surface of the first outer joint member and the spherical outer peripheral surface of the first inner joint member, 
 a curvature center of the track grooves of the first outer joint member and a curvature center of the track grooves of the first inner joint member being offset to opposite sides in the axial direction of the fixed type constant velocity universal joint with respect to a joint center by an equal distance; 
 
 a plunging type constant velocity universal joint comprising:
 a second outer joint member having a cylindrical inner peripheral surface in which eight track grooves extending in an axial direction of the plunging type constant velocity universal joint are formed; 
 a second inner joint member having a spherical outer peripheral surface in which eight track grooves extending in the axial direction of the plunging type constant velocity universal joint are formed, and having a spline hole formed along an axial center of the second inner joint member; 
 eight balls arranged in ball tracks formed by the track grooves of the second outer joint member and the track grooves of the second inner joint member; and 
 a second cage, which has eight pockets configured to receive the balls of the plunging type constant velocity universal joint, and is held in slide contact with the cylindrical inner peripheral surface of the second outer joint member and the spherical outer peripheral surface of the second inner joint member, 
 a curvature center of a spherical portion formed in an outer peripheral surface of the second cage and a curvature center of a spherical portion formed in an inner peripheral surface of the second cage being offset to opposite sides in the axial direction of the plunging type constant velocity universal joint with respect to a joint center by an equal distance; and 
 
 an intermediate shaft comprising:
 an outboard-side spline to be fitted into the spline hole of the first inner joint member of the fixed type constant velocity universal joint; and 
 an inboard-side spline to be fitted into the spline hole of the second inner joint member of the plunging type constant velocity universal joint, 
 
 wherein a ratio PCD BALL (f)/D BALL (f) of a pitch circle diameter PCD BALL (f) of the balls of the fixed type constant velocity universal joint to a diameter D BALL (f) of each of the balls of the fixed type constant velocity universal joint is set from 3.70 to 3.87, 
 wherein a ratio PCD BALL (s)/D BALL (s) of a pitch circle diameter PCD BALL (s) of the balls of the plunging type constant velocity universal joint to a diameter D BALL (s) of each of the balls of the plunging type constant velocity universal joint is set from 3.3 to 3.6, 
 wherein a ratio PCD SPL (f)/D BALL (f) of a pitch circle diameter PCD SPL (f) of the spline hole of the first inner joint member of the fixed type constant velocity universal joint to the diameter D BALL (f) of each of the balls of the fixed type constant velocity universal joint is set from 1.82 to 1.92, and 
 wherein a ratio PCD SPL (s)/D BALL (s) of a pitch circle diameter PCD SPL (s) of the spline hole of the second inner joint member of the plunging type constant velocity universal joint to the diameter D BALL (s) of each of the balls of the plunging type constant velocity universal joint is set from 1.70 to 1.85. 
 
     
     
       2. The rear-wheel drive shaft according to  claim 1 , wherein the fixed type constant velocity universal joint and the plunging type constant velocity universal joint each have a maximum operating angle of 20° or less. 
     
     
       3. The rear-wheel drive shaft according to  claim 1 , wherein the intermediate shaft is hollow.